Valve Application of Thermal Power Plants

1. Open-close type valves of thermal power plants

The general valves for Open-close type thermal power plants include gate valves, globe valves, water pressure test plug valves, check valves, steam traps, etc., as follows:

The globe valve/electric globe valve is installed on water and steam pipelines as an opening and closing device.

The gate valve/electric gate valve is installed on water and steam pipelines as an opening and closing device.

The three-way valve is installed between the pressure gauge and the pressure gauge elbow for the pressure gauge.

The drain valve/electric drain valve is installed on the lower header and centralized down comer of the power station boiler water wall as a boiler drain device.

The check valve is installed on steam and water pipelines as an installation device to automatically prevent medium back flow. Some functions of the check valve can be classified as safety protection.

The steam trap is installed in the steam trap pipeline to discharge condensate to avoid or reduce the scouring and rapid cooling of the equipment by the steam-liquid two-phase flow, causing damage and vibration.

The water pressure test plug valve is installed on the boiler super heater outlet and reheater inlet and outlet steam pipes as an isolation device when the system is subjected to water pressure test. After water pressure test, the internal plugging plate is removed and the guide sleeve is installed to use as a pipeline. The plugging plate can be installed again for repeated use during the next water pressure test.

2. Control-type valves of thermal power plants

In the domestic power industry, it is customary to call the device for regulating water flow and pressure a "regulating valve", which is installed in the spray pipe, water supply pipe, high-pressure drain pipe, water supply bypass, etc. of the boiler's spray water desuperheater to regulate the feed water flow or spray water flow and pressure; the device for regulating steam flow and pressure is called a "pressure reducing valve", which is divided into electric pressure reducing valves and pneumatic pressure reducing valves, and is installed in the boiler's temperature reduction and pressure reduction system, soot blowing system, oil pipeline heating system and air preheater system. However, it is collectively referred to as a "control valve" abroad.

In the thermal system of thermal power units, the turbine bypass system has become an important part of the thermal system of the intermediate reheat unit. The bypass system is mainly composed of two parts: a regulating valve and a control device. Its connection type, function selection, capacity, etc. have a great influence on the operation of the unit. In the bypass system, the valve is one of the important devices. The high-pressure bypass system valves generally include temperature-reducing and pressure-reducing valves, water spray isolation valves and water spray regulating valves. The low-pressure bypass system valves generally include temperature-reducing and pressure-reducing valves and water spray regulating valves. In addition, low-pressure bypass water spray isolation valves and three-stage temperature-reducing water regulating valves can be selected according to user request.

3. Valves for thermal power plants with safety protection

Safety valve is the most common safety protection valve. Its function is to automatically discharge steam when the pressure exceeds the specified value to prevent the pressure from continuing to rise, so as to ensure the safety of boilers and steam turbines. It is mainly installed in the steam drum or steam-water separator, superheater outlet, reheater outlet, deaerator, high and low steam-water side of the power station boiler, industrial steam extraction pipeline, heating pipeline, etc.

The electromagnetic relief valve is a protective device to prevent the steam pressure in the boiler from exceeding the specified value. It opens before the safety valve is activated to discharge excess steam to protect the normal operation of the boiler under the specified pressure. At the same time, it reduces the number of actions of the safety valve and extends the service life of the safety valve.

The pneumatic quick-start valve is used as a device for automatically and quickly cutting off the medium in the boiler oil, water and steam systems. The circulating pump outlet valve is installed at the outlet of the boiler circulating pump. It has the functions of a stop valve and a check valve, which can be closed and prevent the medium from flowing back. The locking valve is installed on the superheater and reheater water spray pipes and is used as a quick opening and closing device. These types of valves can be classified as either safety protection or open-close type, among which pneumatic quick-start valves and locking valves have quick closing or quick opening characteristics.

Pressure relief valves are devices that prevent the pressure of the liquid medium in the equipment from rising above the allowable value and ensure the safe operation of the equipment. They are generally used on the water side of the high-pressure heater, the inlet of the deaerator pump, the inlet of the condensate, the inlet of the feed pump, etc.

The extraction check valve is used in the steam turbine extraction, heating and other systems to prevent the pressure in the steam turbine from suddenly decreasing when the steam turbine unit is suddenly unloaded, and the steam in the extraction pipe and each heater flows back into the steam turbine to cause the steam turbine blades to break and the steam turbine generator to be destroyed. It also prevents the heater system pipeline from leaking and causing water to enter the steam turbine from the extraction pipeline and cause water hammer accidents, so as to protect the safe operation of the steam turbine.